Internal combustion engines are used in a variety of applications, such as lawnmowers, generators, pumps, snow blowers, and the like. Such engines usually have fuel tanks coupled thereto to supply fuel to the engine through a supply line. It is desirable to reduce emissions from devices powered by internal combustion engines. Even when the engine is not being used, the engine can release emissions of hydrocarbons or gasoline resulting from daily ambient temperature changes. Such emissions are known as “diurnal” emissions. To help reduce emissions from the engine, it is known to provide internal combustion engines with fuel shutoff devices that block the flow of fuel to the engine upon engine ignition shutdown. Without such a shutoff device, fuel is wasted, and unburned fuel is released into the environment, thereby increasing hydrocarbon exhaust emissions. Likewise, the presence of unburned fuel in the combustion chamber may cause dieseling. When the engine is not operating, pressure buildup in the fuel tank caused by increased ambient temperatures can force fuel into the engine, where the fuel can be released into the atmosphere.
It is also desirable to reduce emissions from the fuel tank. Fuel tanks are typically vented to the atmosphere to prevent pressure buildup in the tank. While the engine is operating and drawing fuel from the fuel tank, the vent in the fuel tank prevents excessive negative pressure inside the tank. While the engine is not operating (i.e., in times of non-use and storage), the vent prevents excessive positive pressure that can be caused by fuel and fuel vapor expansion inside the tank due to increased ambient temperatures. Fuel vapors are released to the atmosphere primarily when a slight positive pressure exists in the tank.
One method of venting fuel tanks includes designing a permanent vent into the fuel tank cap. Typically, the fuel tank is vented via the threads of the screw-on fuel tank cap. Even when the cap is screwed tightly on the tank, the threaded engagement does not provide an airtight seal. Therefore, the fuel tank is permanently vented to the atmosphere. Another method of venting fuel tanks includes the use of a vent conduit that extends away from the tank to vent vapors to a portion of the engine (i.e., the intake manifold) or to the atmosphere at a location remote from the tank.